1. Field of the Invention
The invention relates to coatings for polymeric substrates formed from unsaturated monomers and more particularly to optically clear, abrasion resistant, adherent coatings particularly suitable for ophthalmic products such as CR-39 lenses.
2. Description of the Prior Art
Polymeric ophthalmic lenses have become increasingly popular recently due to their fine optical properties, dimensional stability, impact resistance, light weight, etc. One serious disadvantage, nevertheless, to polymeric ophthalmic lenses, has been their susceptibility to scratching, particularly compared to traditional glass lenses.
Much research has been devoted to providing coatings for polymeric lenses to improve their abrasion resistance. To date, however, none of the resultant coatings has proven totally successful as evidenced by their lack of commercial acceptance. This is probably because of the stringent requirements in optical and mechanical properties necessary in such coatings.
An example of one type of coating provided to solve this problem is given in U.S. Pat. No. 3,637,416 to Misch et al. The coatings described in the Misch et al. patent are applied by coating a plastic lens with a bonding or coupling film comprising an organic silicon compound and also coating it with a silica or silica gel. The preferred coating technique is a two-step technique, although both coatings can be applied simultaneously. Even in the one-step coating technique, however, the combination of both an organic silicon compound and a silica or silica gel forming compound is present.
Still other attempts are described in U.S. Pat. No. 3,713,880 to Krekeler et al. The coatings described by this patentee contain alkyl silicates, trifunctional and/or bifunctional organosilanes and antistatic additives.
Abrasion resistant ophthalmic coatings formed from vinyltri(lower alkoxy)silanes are also described by French et al. in Ser. No. 376,505, filed July 5, 1973.
Despite the large amount of prior research, there is still a need for a process of forming optically clear coatings on polymeric substrates which have even better scratch resistance and adhesion.